The present invention relates to an improvement on a metal mold for vulcanization of tires.
The conventional metal mold for this purpose is shown in FIGS. 1 through 4, which illustrate, in cross section, operation stages of a vulcanization press machine for tires, which is referred to as a bagomatic press, on which a conventional metal mold is mounted. The first stage shown in FIG. 1 is a vulcanization stage in which a green tire is disposed between an upper half mold 10, a lower half mold 12, an upper bead ring 11, a lower bead ring 13 and a bladder 14 supported by the bead rings and is heated under pressure, resulting in a vulcanization tire 15.
In the second stage in FIG. 2, the press machine is opened after the vulcanization so that the upper half mold 10 secured by bolts 16 to an upper platen 17 which is, in turn, secured to a platen shaft 18 fixed to a top link 25 is separated from the tire 15. The opening and closing of the press machine is performed by lifting and lowering platen shaft 18, respectively, by means of a suitable mechanism.
In the third stage in FIG. 3, the lower bead ring 13 secured to an upper part 19 of a cylinder 20 having a piston rod 21 is moved upwardly by driving the cylinder 20 upwardly to separate the tire 15 from the lower half mold 12.
Then, in the fourth stage in FIG. 4, the piston rod 21 of the cylinder 20 is driven upwardly to push the upper bead ring 11 up to thereby stand up the bladder 14. Consequently, the bladder 14 is separated from the tire 15, allowing the latter to be removed from the press machine.
In the conventional pressing process including the four stages shown in FIGS. 1 through 4, however, there is a problem in that, in the second stage shown in FIG. 2, the tire 15 tends to be separated unexpectedly from not the upper half mold 10 but the lower half mold 12 and to move upwardly with the upward movement of the platen 17, with the probability of occurence of the latter being about 5%. In such case, the removal of the tire 15 from the upper half mold 10 is performed by manually inserting a plate between the upper half mold 10 and the tire 15 and prying it loose. This removal requires a substantial amount of labour.
In order to resolve this problem, it has been usual to put, on an inner surface of the upper half mold 10, a medium which facilitates a separation of the upper half mold 10 from the tire 15. This resolution is, however, not so effective and there is still a considerable time loss.